Institute for Systems Research Technical Reports
Permanent URI for this collectionhttp://hdl.handle.net/1903/4376
This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.
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Item Robust Control of Set-Valued Discrete Time Dynamical Systems(1995) Patel, N.S.; Baras, J.S.; ISRThis thesis deals with the robust control of nonlinear systems subject to persistent bounded non-additive disturbances. Such disturbances could be due to exogenous signals, or internal to the system as in the case of parametric uncertainty. The problem solved could be viewed as an extension of l1- optimal control to nonlinear systems, however, now under very general non-additive disturbance assumptions. We model such systems as inclusions, and set up an equivalent robust control problem for the now set- valued dynamical system. Due to the fact that inclusions could arise from other considerations as well, we solve the control problem for this generation class of systems. The state feedback problem is solved via a game theoretic approach, wherein the controller plays against the plant. For the output feedback case, the concept of an information state is employed. The information state dynamics define a new infinite dimensional system, and enable us to achieve a separation between estimation and control. This concept is extended to the case of delayed measurements as well. For motivational purposes, we formally derive the information state from a risk-sensitive stochastic control problem via small noise limits. In general, the solution to the output feedback case involves solving an infinite dimensional dynamic programming equation. One way of avoiding this computation in practice is to consider certainty equivalence like controllers. This issue is considered, where we generalize the certainty equivalence controller to obtain other non-optimal, but dissipative output feedback policies. The approach followed yields both necessary and sufficient conditions for the solvability of the problem. We also present some applications of the theory developed.Item A Framework for Robust Run by Run Control with Lot Delayed Measurement(1995) Baras, John S.; Patel, N.S.; ISRThis paper considers the run by run control problem. We develop a framework to solve the problem in a robust fashion. The framework also encompasses the case where the system is subject to delayed measurements. Recent results available for the control of such systems are reviewed, and two simple examples are presented. The first example is based on the end-pointing problem for a deposition process, and is subject to noise which has both Gaussian and uniform components. The second one is concerned with rate control in a LPCVD reactor.Item Nonlinear HControl with Delayed Measurements(1995) Baras, John S.; Patel, N.S.; ISRThis paper considers the nonlinear Hcontrol problem for systems subject to delayed measurements. Necessary and sufficient conditions for the solvability of the problem are presented. We employ the concept of an information state to achieve separation between estimation and control. In particular, the information state derived is no longer the ﲷorst case cost to come function. We also briefly discuss certainty equivalence for systems with delayed measurements.Item Reduced Complexity Output Feedback Nonlinear HControllers and Relation to Certainty Equivalence(1995) Baras, John S.; Patel, N.S.; ISRIn this paper, we consider the problem of constructing reduced complexity controllers for output feedback nonlinear Hcontrol. We give sufficient conditions, under which the controllers so obtained, guarantee asymptotic stability of the closed-loop system when there are no exogenous inputs. The controllers obtained are non-optimal in general. However, in case optimality holds, we show that these controllers are in fact the certainty equivalence controllers.Item Robust Control of Set-Valued Discrete Time Dynamical Systems(1994) Baras, John S.; Patel, N.S.; ISRThis paper presents results obtained for the robust control of discrete time dynamical systems. The problem is formulated and solved using dynamic programming. Both necessary and sufficient conditions in terms of (stationary ) dynamic programming equalities are presented. The output feedback problem is solved using the concept of an information state, where a decoupling between estimation and control is obtained.Item Information State for Robust Control of Set-Valued Discrete Time Systems(1994) Baras, John S.; Patel, N.S.; ISRIn this paper, we construct the information state for robust output feedback control of set-valued discrete time dynamical systems. The information state is obtained as the small noise limit of an appropriate risk-sensitive stochastic control problem. It is possible to obtain this limit by an extension of the Vardgan-Laplace lemma. Finally, the relationship between the information state, and the indicator function of feasible sets is examined.Item Intelligent Process Control(1993) Patel, N.S.; Baras, J.S.; ISRIt is often observed that human experts can tune the parameters of a controller based on their knowledge and experience, rather than on complicated algorithms. In fact, more often than not, they have only a vague idea of the process model. An attempt is made here to create a fuzzy-logic based expert which would emulate such behavior. The expert is, specifically designed to tune the gains of a Proportional-Integral-Derivative (PID) controller, applied to stable dominant pole plants having large rise times. It is observed, that a number of plants found in the chemical process industry can be suitable modeled as such systems. a rule base for the expert was developed after analysis and simulation studies. Attempts have been made to keep the rules as few and simple as possible. At no point is any attempt made to estimate the parameters of the plant model. The expert observes only the output from the plant. Results of the application of the expert to a second order plant, to the separator temperature control loop of the Tennessee Eastman problem, and to a third order plant are presented. The expert is found to successfully tune the PID gains, and the results provide encouragement for the creation of such experts which can handle a class of plants.,Item Derivation of Fuzzy Rules for Parameter Free PID Gain Tuning(1993) Baras, John S.; Patel, N.S.; ISRIn this paper, rules for a fuzzy logic based PID tuner (expert) for stable dominant pole plants with large rise times are derived. Applications of the expert to separator temperature control, and to pH control are presented. It is observed that the expert can successfully tune the PID gains without requiring any process identification.